add set_tags_batch, set_tags + constructor takes added options

[halloleo]

Hi sven

Here my go at the set_tags feature:

new feature: methods set_tags_batch & set_tags allow to write metadata
tags to image files. implement a test for this in test_exiftool.py.

enhancement: constructor takes added options which get passed to the
stay-open instance of exiftool.

Cheers, Leo

ps: Please excuse if anything is strange in the code or in my github use. This is my first github check-in!

[smarnach]

Thanks for your efforts – I really appreciate your suggestions and I will include both of the suggested features. However, I won't merge the patch as it is – I added a few remarks regarding the problems I see. Please allow for a few days to get this done. I have some patches ready for writing tags that still need tests, but I will use the addedargs feature from this patch.

[halloleo]

Hi Sven, I have added methods for keyword modification. Internally they don't use the JSON input, but that can be changed.

The mode constants KW_... are on the top level, not inside the object. I'm not sure whether that's the best choice.

Error checking is still fragile.

[alexbruy]

This pull request also solves issues #9 and #2

[mairsbw]

Any plan to merging this or adding this functionality? It's been 3 years, so I assume no, but this would be very helpful to me.